Skin hydration is an interesting term that has great consumer and scientific meaning. From a consumer standpoint, well-hydrated skin is smooth and soft. Consumers seem to equate skin wrinkling with dehydration as a result of water loss. While this may be true in some individuals and facial areas, in most cases, skin wrinkling is due to loss of collagen and subcutaneous tissue. Fine lines, especially around the eyes, may be worsened by skin dehydration, but facial wrinkles and folds cannot be corrected by increasing skin water content.
From a scientific standpoint, skin hydration is an important parameter to measure for confirming moisturizer benefits and lack of cleanser skin barrier damage. Skin hydration is measured with a corneometer, which uses electrical current conductivity to assess skin water content. The probe puts low voltage electricity into the skin and measures the current that is received at the sensing portion of the probe. This is directly related to skin water content, since water serves as the conductor. The skin must be freshly washed, completely dry, and acclimated to the surrounding environment. Usually, subjects are asked to sit at the research for 30 minutes prior to performing measurements to ensure skin equilibrium. While the number obtained will vary from individual to individual, the most important observation is the change over time as the moisturizer or cleanser is used.
When evaluating a product designed to improve skin hydration, a baseline corneometry measurement is obtained and the subject will use the product twice daily for 2 weeks, which is one stratum corneum turn over cycle. The subject will return to the research center for a repeat corneometry measurement at week 2 followed by discontinuation of the moisturizer. A third measurement will then be taken one week after moisturizer discontinuation, known as the regression period. The idea of the regression period is to determine the halo effect of the moisturizer after the product has been discontinued. A good moisturizer formulation will show increased corneometry measurements one week after discontinuing product application over baseline.